There is substantial evidence that in autism cerebral cortical information processing is abnormal in the "high-order" areas that underlie language and social interaction skills, and also in the "lower-order areas" which accomplish the initial processing of thalamocortical afferent activity evoked by sensory stimulation. Abnormalities in the response of primary sensory cortex in autism have been convincingly demonstrated using psychophysical testing procedures and neurophysiological recording methods. For example, autism subjects routinely exhibit hyperarousal to sensory input, and a decreased ability to select among competing sensory inputs. Furthermore, the regions of cortex devoted to stimulus-driven sensory processing display excessive responsivity in individuals with autism, and exhibit little-to-no specificity in their response to either the location or modality of a sensory stimulus.
One of the major issues in autism being studied today is its heterogeneity. That is, not all people with autism have autism because of the same genetic and environmental impacts. Understanding the differences in the way the brain processes information within this subject population may prove to be essential for determining what treatment, whether it be behavioral or pharmacological, should be administered. Several tests to measure the temporal integrative capacity of subjects were developed. The graph at the above left is exemplary of the results obtained from one of these tests, in which subjects match stimuli that are being modulated (one vibrotactile stimulus is getting larger, the other is getting smaller; Francisco et al 2011; Zhang et al 2011) and it demonstrates that the autism population that was sampled (n=45) clustered into two distinct groups. Other tests that were administered also resulted in the data from these two groups segregating distinctly.
Validation with fMRI: A subset of the autism population that was studied via sensory testing participated in a parallel functional Magnetic Resonance Imaging (fMRI) study in which the brain was imaged in response to different types of stimulus conditions. Comparisons of the responses in the brain to these conditions with the newly developed sensory metrics demonstrate a high degree of correlation (figure at left; R2=0.80). Additionally, the fMRI metric obtained categorized the subjects into the same 2 groups that were detected via sensory metrics. Traditional sensory metrics (such as threshold testing), on the other hand, failed to yield such a correlation with the fMRI metric and did not show a distinct segregation of the two populations (R2 of 0.12) The high correlation between fMRI and the sensory metric could actually be higher with a larger data sample and if the fMRI data could be obtained at higher resolution. It is important to keep in mind that there are currently no non-invasive means for evaluating activity in the brain that are as sensitive to subtle changes in sensory experience as sensory percept is. In other words, this pilot study demonstrated good correlation between a crude measure of brain activity (fcMRI) vs. a highly refined measure of brain activity (sensory percept).
We are currently evaluating the cerebral cortical information processing capacity of individuals with autism through collaborations with the UNC Neurodevelopmental Disorders Research Center.
Collaborations